AP Review Chapters 16-18

Fast Facts The role of DNA in heredity was first studied by using bacteria and viruses. Griffith (1928) was studying streptococcus pneumonia. Transformation: a change in genotype and phenotype due to the assimilation of external DNA by a cell. Avery (1944) purified various chemicals from the heat killed bacteria to recreate Griffith’s experiment. Only DNA worked.

Fast Facts Hershey and Chase performed experiments showing that DNA is the genetic material of T2 (a type of phage).

Fast Facts The monomer of nucleic acids are nucleotides - each consists of 3 parts: a nitrogenous base, a pentose sugar called deoxyribose, and a phosphate group. - the base can be adenine (A), thymine (T), cytosine (C), or guanine (G).

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Fast Facts A series of enzymes carries out the steps of DNA replication DNA Polymerase: enzyme that catalyzes the elongation of new DNA DNA strands line up in an antiparallel arrangement 5’-------------3’ 3’-------------5’

Fast Facts DNA polymerase adds nucleotides only to the free 3’ end of a growing DNA strand. A new DNA strand can elongate only in the 5’  3’ direction. - leading strand: DNA strand made by this mechanism; works toward the replication fork

Fast Facts To elongate the other strand, polymerase must work in the direction away from the replication fork. This is the lagging strand - Okazaki fragment - DNA ligase: joins Okazaki fragments to make a single DNA strand

Fast Facts Transcription and Translation are the two main processes linking genes to proteins - transcription is the synthesis of RNA under the direction of DNA - translation is the actual synthesis of a polypeptide, which occurs under the direction of mRNA

Fast Facts Nucleotide triplets specify amino acids - there are only 4 nucleotides to code for the 20 amino acids - triplet code: the genetic instructions for a polypeptide chain are written in the DNA as a series of three nucleotide words

Fast Facts - the codon AUG has a dual function: it codes for the amino acid Methionine (Met) and it functions as a “start” signal, or initiation codon - RNA polymerase: connects the RNA nucleotides as they base-pair along the DNA template

Fast Facts In translation, the cell interprets the genetic message and builds a protein accordingly - transfer RNA (tRNA): transfers amino acids from the cytoplasm’s amino acid pool to a ribosome - contains an anticodon that is complementary to the mRNA codon

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Sample Question Describe the steps of protein synthesis, beginning with the attachments of a messenger RNA molecule to the small subunit of a ribosome and ending with the release of the polypeptide from the ribosome. Include in your answer a discussion of how the different types of RNA function in this process.

Fast Facts A virus is a genome enclosed in a protective coat - a virus can be a DNA virus or an RNA virus depending on the kind of nucleic acid - the protein shell that encloses the viral genome is called the capsid Some viruses have viral envelopes, membranes that cloak their capsids - derived from the membrane of a host cell

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Fast Facts Phages replicate using either the lytic or lysogenic cycle Lytic cycle: reproductive cycle that culminates in the death of the host. - during the last stage of the cycle the cell breaks open (or lyses) and releases the phages that were produced Lysogenic cycle: replication of the phage genome without destroying the host

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Fast Facts Retrovirus - most complicated reproductive cycle of viruses - refers to the reverse directional flow of the genetic information - contain reverse transcriptase: transcribes DNA from an RNA template - RNA  DNA directional flow - DNA integrates as a provirus in the host cell

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Fast Facts The control of gene expression enables bacteria to adjust their metabolism to environmental change The lac operon: regulates the synthesis of the enzymes needed to metabolize lactose.

Fast Facts -w/out lactose, no emzymes are made for metabolism - the regulatory gene, lacI is producing a repressor (prevents the transcription process) which blocks the RNA polymerase from working

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Fast Facts - when lactose is present, an inducer binds to the repressor making it inactive - RNA polymerase can then begin the transcription process and the gene can be expressed

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Sample Questions Describe the operon hypothesis and discuss how it explains the control of messenger RNA production and the regulation of protein synthesis in bacterial cells.